The present invention relates to a heat exchanger for a first and a second medium flow, comprising flat tubes which have internal tins formed from zigzag-shaped sheet metal plate, said tubes having a thermally conductive connection to at least one duct for the one medium flow.
Heat exchangers for EGR-gas are used, for example, in diesel engines for heavy vehicles and are exposed to very large temperature changes as the working temperature varies greatly from cold starting to full load. These temperature changes can give rise to problems in the form of fatigue and damage in the metal structure, which on the one hand can lead to impaired heat exchange and on the other can have a negative effect on the gas flow through the heat exchanger.
It is desirable to provide a heat exchanger for EGR-gas, which is more resistant to temperature changes and is thereby more reliable.
To this end, the heat exchanger according to the invention is characterized in that the fins are fixed only to the one longitudinal side of each tube, and that there is a gap between the fins fixed on the one longitudinal side and the opposite longitudinal side of the tube. Forming the tubes in this way means that as the fins heat up they have scope to expand into said gap, towards the opposite tube wall.